What is a GPX file?

GPX is a GPS eXchange format to interchange GPS related data with devices from different manufacturers and between different software programs.

In GPX, a collection of points, with no sequential relationship (the
county towns of England, say, or all Skyscrapers in New York), is deemed
a collection of individual waypoints. An ordered collection of points
may be expressed as a track or a route.
Conceptually, tracks are a record of where a person has been, routes
are suggestions about where they might go in the future. So, for
instance, there might be timestamps for each point in a track (because
someone is recording where and when they were there), but
timestamps for each point in a route are unlikely to be provided,
because the author is suggesting it, and nobody might ever have
travelled it.

The minimum properties for a GPX file are latitude and longitude for a
single waypoint. All other variables are optional.

Sample GPX Document

The following is a truncated (for brevity) GPX file produced by a
hand-held GPS unit. This document does not show all functionality which
can be stored in the GPX format – for example, there are no waypoints or
extensions, and this is part of a track, not a route – but the purpose
is to serve as a brief illustration.

GPX, or GPS eXchange Format is an
XML schema designed as a common GPS data format for software
applications.

It can be used to describe waypoints, tracks, and routes. The format
is open and can be used without the need to pay license fees. Its tags
store location, elevation, and time and can in this way be used to
interchange data between GPS devices and software packages. Such
computer programs allow you for example to view your track, project your
track on satellite images (in Google Earth), annotate maps, and tag
photographs with the geolocation in the Exif metadata.